#include<iostream>
#include<algorithm>
#include<vector>
#include<unordered_map>
using namespace std;
int main()
{
	int n;
	cin >> n;
	vector<int> vc(n);
	vector<int> v(n);
	unordered_map<int, int> mp;
	bool vis = false;
	int ans = -1;
	for (int i = 0; i < n; i++)
	{
		cin >> vc[i];
		mp[vc[i]]++;
		if (mp[vc[i]] == 1)
		{
			v.push_back(vc[i]);
		}
	}
	for (int i = 0; i < v.size(); i++)
	{
		if (mp[v[i]] == 1)
		{
			ans = v[i];
			break;
		}
	}
	if (ans != -1) {
		cout << ans;
	}
	else {
		cout << "None";
	}
	return 0;
}